Measurement of Damping in Composite Structure Assembly at Cryogenic Temperatures

Abstract

The J ames Webb Space Telescope will be a large infrared telescope with a 6.5m primary mirror. The telescope structure will operate in cryogenic temperatures below 50 Kelvin ( -370 deg F) . In order to meet its mission objectives at these temperatures, t he struc ture must maintain a strict thermal and dynamic stability during imaging operations . To verify that stability requirements are a chievable, a developmental test article of the J WST backplane was constructed. The carbon composite test article underwent a ser ies of cryogenic tests inside a thermal vacuum chamber located at NASA ’s Marshall Space Flight Center (MSFC) in Huntsville, Alabama . The focus of this paper is on testing performed to characterize damping levels at cryogenic temperatures; thereby serving t o lower uncertainty in analytical model ing and predictions of the telescopes jitter performance. Prior to this testing, empirical data did not exist to validate damping assumptions used in analytical models 1-2 . At the conclusion of the test, the data showe d a considerable decrease in damping levels as the structure reached cryogenic temperatures. The structural damping of the test article was successfully characterized from room temperature down to the operational cryogenic temperature range .